Freight trains and passenger trains generally include a locomotive that provides the motive power for a train. Having no payload capacity of its own, the sole purpose of the locomotive is to move the train along the tracks. Typically, the locomotive may use an engine to drive a primary power source, such as, a main generator or an alternator. Converting mechanical energy into electrical energy, the primary power source provides power to traction motors in order to drive wheels of the locomotive. The traction motors propel the train along the tracks.
One or more wheels of the locomotive can become locked due to various reasons, such as gear train issues, inadvertent application of the parking brakes during operation, etc. In order to detect a locked wheel, locomotives may have locked wheel fault detection systems. A locked wheel fault detection system may use speed probes to monitor a speed of each of the traction motors. For example, when one of the speed probes detects a speed of zero, while the other speed probes detect a nonzero speed, the system may detect a locked wheel.
However, in some instances, a traction motor pinion may be slipped, resulting in the traction motor becoming mechanically decoupled from the gear case and wheel axle. Due to the decoupling of the wheel axle from the traction motor, the locked wheel fault detection system may not have the ability to detect a locked wheel. In particular, the system has no feedback related to the actual speed of the wheel axle that is decoupled from the traction motor with the slipped pinion.
A method for detecting a potentially locked wheel axle on a vehicle propelled by an AC motor is disclosed in U.S. Pat. No. 6,532,405, entitled, “Method for Detecting a Locked Axle on a Locomotive AC Traction Motor.” The '405 patent describes conducting a speed test by estimating axle speed and comparing the estimated axle speed to a measured vehicle speed. The existence of a potential locked axle condition is determined based on the comparison of estimated axle speed to measured vehicle speed. While effective for detecting a potential locked axle condition, the '405 method does not detect whether a traction motor pinion is slipped. Improvements are desired to determine whether a traction motor is mechanically decoupled from a wheel axle.